(1) Field of the Invention
The present invention relates to an imaging device, especially to a technique to produce an image with a resolution lower than an original resolution of the imaging device and excellent image quality.
(2) Description of the Related Art
In recent years, solid-state imaging elements have a larger number of pixels. Solid-state imaging elements with a resolution exceeding megapixel, i.e. one million pixels are now used even in simple devices such as compact cameras and mobile telephones.
Accordingly, still pictures with a very high resolution can be taken with such simple devices. On the other hand, images with a resolution lower than an original resolution of a solid-state imaging element are necessary to be used for individual frame pictures of a moving picture and images to be attached with e-mails. Accordingly, an operation for reducing a resolution has become indispensable.
As a technique to produce an image with a target resolution lower than an original resolution of a solid-state imaging element, it is known to discard some of the pixels of the solid-state imaging element. A resolution of an image produced by this technique is one N-th of the original resolution of the solid-state imaging element, where N is an integer.
If the resolution of the image produced by the technique of discarding pixels is not equal to the target resolution, a zoom operation is further performed to produce the image with the target resolution.
A technique to perform such a zoom operation with minimizing worsening in image quality is, for example, disclosed in Japanese unexamined patent application publication No. 2002-374407 (hereinafter referred to as a patent document 1).
However, such a conventional technique of discarding pixels and performing a zoom operation can not produce an image with excellent image quality in addition to a resolution lower than an original resolution of a solid-state imaging element. This is because the discarding of pixels causes large aliasing noise to be generated.